1. Field of the Invention
The present invention relates to a variable valve apparatus of an internal combustion engine, which varies the phase of an intake valve or an exhaust valve.
2. Description of the Related Art
Many reciprocating engines mounted in automobiles include a variable valve apparatus for changing the phases of an intake valve and an exhaust valve, for reasons of engine gas emission countermeasures, fuel consumption reduction and the like.
Many of such variable valve apparatuses employ a structure in which the phase of a cam formed on a camshaft is replaced with an oscillating cam in which a base circular zone and a lift zone are ranging. Specifically, a structure is employed in which an oscillating range of the oscillating cam is changed, whereby a valve opening period and a valve lift amount of the intake valve and the exhaust valve driven via a rocker arm are varied continuously.
In order to improve a pumping loss, a structure is proposed in Jpn. Pat. Appln. KOKAI Publication No. 2003-239712 in which a transmission arm is interposed between a cam and an oscillating cam, and the transmission arm is oscillatably supported by a control shaft. Specifically, the transmission arm is moved by the turning displacement of the control shaft. A contact position of transmission arm and the cam is changed by moving the transmission arm. By changing the contact position of the transmission arm and the cam, the valve characteristics, that is, a valve opening period, valve open-close timing and a valve lift volume are continuously varied.
Under this kind of variable valve apparatus, variable response suited for a vehicle operating condition is requested. Specifically, when the valve lift volume is varied from a low valve lift volume to a high valve lift volume which is greater than the low valve lift volume, under which the vehicle is accelerated. As a result, it is enough that the valve lift volume is varied corresponding to acceleration. But conversely, in many cases in which the valve lift volume is varied from a high valve lift volume to a low valve lift volume, quick response is requested.
For example, when engine brakes are applied to a vehicle which carries out high rotating operation, a throttle valve is closed while maintaining the high valve lift set by the relevant high rotating operation in an engine equipped with a variable valve apparatus. Engine braking effects are generated by a pump loss generated in such a case. In this case, engine rotation is decreased due to the pump loss. When the effects of the engine brake are cancelled, it is requested to immediately vary the valve lift from high to low.
In order to secure this kind of high response with the variable valve apparatus as shown in Jpn. Pat. Appln. KOKAI Publication No. 2003-239712, it is required to use an actuator with a large capacity for an actuator which rotatably operates the control shaft.
However, the actuator with a large capacity is large. Therefore, the size of the variable valve apparatus is increased. The weight is increased and or energy consumption tends to increase. In addition, the increased size of the actuator may give rise to problems of degraded engine mountability to vehicles or increased engine weight.